Export to .STL Format In Correct Scale - Inches
By default Blender uses 1 unit = 1 meter even if you change the units in Blender to Imperial - Inches. That change only affects the GUI display, not the internal representation. According to Wikipedia, STL is unitless so use a scale of 39.37 to convert from meters to inches when you export, or tell the program you import into the file is in meters.
Basically, in Blender's Scene tab, set the Unit System to whatever you're comfortable with, choose whatever length you like, but leave &quot;Unit Scale&quot; set to 1.0. This leaves Blender internally using Meters, this is a good thing, because the unit system is a little strange sometimes.
When exporting your STL, set the Transform Scale to 39.37 (to convert meters to inches) and don't bother with &quot;Scene Units&quot; check box, it multiplies by the value in &quot;Unit Scale&quot; which we purposefully left at 1.0.